;; a silly struct and two silly functions that use it:
(defstruct person name)

(defun print-hello (person)
  (let ((name (string-upcase (person-name person))))
    (format t "HI, ~A!" name)))

(defun make-name-upcase (person)
  (let ((name (string-upcase (person-name person))))
    (setf (person-name person) name)))

;; first use case, name is just a string:
(defvar bob (make-person "Bob"))
(print-hello bob)
(make-name-upcase bob)

;; change name to be an array of strings:
(defvar bob (make-person (vector "Bob" "Featherstone")))